Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The classical signs of acute inflammation are pain, heat, redness, swelling, and loss of function. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process. In an inflammatory response, cytokines and chemokines are released from various cell types, which increases blood vessel permeability, upregulates endothelial receptors, and increases egress of various cells of the innate and adaptive immune system to enter surrounding tissue. In autoimmune diseases, the immune system triggers an inflammatory response when there are no harmful stimuli, thus causing damages to normal tissues.
Inflammation can be a localized reaction of live tissue due to an injury, which may be caused by various endogenous and exogenous factors. The exogenous factors include physical, chemical, and biological factors. The endogenous factors include inflammatory mediators, antigens, and antibodies. Endogenous factors often develop under the influence of an exogenous damage. An inflammatory reaction is often followed by an altered structure and penetrability of the cellular membrane. Endogenous factors, namely, mediators, antigens, and autogens define the nature and type of an inflammatory reaction, especially its course in the zone of injury. In the case where tissue damage is limited to the creation of mediators, an acute form of inflammation develops. If immunologic reactions are also involved in the process, through the interaction of antigens, antibodies, and autoantigens, a long-term inflammatory process will develop. Various exogenous agents, for example, infection, injury, radiation, also further the course of inflammatory process on a molecular level by damaging cellular membranes which initiate biochemical reactions.
Infection is the invasion of a host organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to these organisms and the toxins they produce. The disease-causing agents can be infectious agents such as viruses, viroids, and prions, microorganisms such as bacteria, nematodes such as roundworms and pinworms, arthropods such as ticks, mites, fleas, and lice, fungi such as ringworm, or macroparasites such as tapeworms. Symptoms of an infection can be signs affecting the whole body, such as fatigue, loss of appetite, weight loss, fevers, night sweats, chills, aches and pains, or signs specific to individual body parts, such as skin rashes, coughing, or a runny nose. Hosts can fight infections using their immune system. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response. Infections can cause host tissue damage. In certain cases, the host's protective immune mechanisms are compromised, and the organism inflicts damage on the host. In some cases, microorganisms cause tissue damage by releasing a variety of toxins or destructive enzymes.
Targeted imaging for targeted therapy—using radiolabeled forms of targeted therapeutic agents for PET imaging—is much advocated for the future of medical imaging & drug development, by the National Cancer Institute and others. (National Cancer Institute, U.S. National Institutes of Health. A workshop regarding what in-vivo molecular imaging probes are needed to support future translational studies in cancer therapeutics. Paper presented at: Strategies for Imaging Priority Targets, 2002; Frankfurt, Germany; Weber W A et al. Nat Clin Pract Oncol. 2008; 5(1):44-54; Workman P et al. J Natl Cancer Inst. 2006; 98(9):580-598; Workman P et al. Ann N Y Acad Sci. 2007; 1113:202-216). The unique potential of PET microdose studies in development of drugs as therapeutic and/or diagnostic imaging agents is recognized by the US FDA and others. A review of published PET micro-dosing studies is provided by Wagner et al (Wagner C C et al. Curr Opin Drug Discov Devel. 2008 January; 11(1): 104-10).
Various agents for infection and/or inflammation imaging are currently in clinical use (Petruzzi et al. Semin. Nucl. Med. 2009; 39(2): 115-123). However, more imaging agents will provide additional options for imaging, diagnostics, and treatment of infection and/or inflammation.